Sorry to hear the news. Remember, the point of communication is to change YOU, not him. So, tell him what you want to. But PLEASE don't find his plane ticket. Geez. You don't have to swallow this and act like everything is great. It isn't. And, remember, email works.
"Gabe,
Given our conversation today, I see that our current romantic relationship has reached its end. I’m saddened and disappointed, I had hoped to build a great new relationship with you that worked for all of us, but things did not work out that way. I will be fine. I chose to take the emotional risk and it didn't pay off this time for me. I hope you find stability and happiness in California.
That being said, given our relationship is over, it does not work for me to take care of your plane ticket or other personal needs. I require my own emotional and physical space. It is not fair to me or Marc or you to allow our current arrangement to continue – it is clear that Marc and I both want more from you than you want to share. That isn’t good for anyone. We need to go to a strictly business/co-parent relationship ASAP. So, it is important that you find elsewhere to stay immediately while you make your other travel arrangements.
Please take some time to talk to Marc. He will likely feel very hurt and lost as he has really thrived with your presence. So, whatever love and support you can share with him would be great."